High-speed indenting recorder

ABSTRACT

An electromechanical indenting recorder consists of a solenoid coil, a ferromagnetic housing about the coil, and a nonferromagnetic plunger that moves inside the core. The plunger has a ferromagnetic cover attached thereto which cover extends at least in part over the core and the housing forming an annular airgap therebetween. The cover serves to stop the movement of the plunger by contacting said housing, and the core cover, core and housing form a magnetic circuit with the airgap. An indenting knife is carried by one end of the plunger opposite from the cover and in operation serves to make a series of indentations, usually in a binary code form, in a suitable receptor sheet such as a pocket credit card. The plunger and cover are very light such that they can move rapidly under the influence of the magnetic field created when the solenoid is energized. The solenoid is initially energized and midway through the stroke of the plunger the driver current is cut off and the solenoid circuit remains closed through a diode such that the plunger continues accelerating towards the stop position under the influence of the decaying field of the magnetic circuit. The efficiency of the device is high and the excess heat generated is at a minimum.

United States Paten [151 3,644,932 Wallace et al. 1 Feb. 22, 1 972 [54] HIGH-SPEED INDENTING RECORDER [57] ABSTRACT [72] Inventors: John G. Wallace, Ashland; Edmund An electromechanical indenting recorder consists of a sole- Schreiner, Newtonville, both of Mass. noid coil, a ferromagnetic housing about the coil, and a nonferromagnetic plunger that moves inside the core. The plunger [73] Asslgnee' Synergisflcs has a ferromagnetic cover attached thereto which cover ex- [22] Filed: Oct. 8, 1969 tends at least in part over the core and the housing forming an annular airgap therebetween. The cover serves to stop the [2]] A 864846 movement of the plunger by contacting said housing, and the core cover, core and housing form a magnetic circuit with the [52] US. Cl. ..346/77, 83/577, 317/123, airgap. An indenting knife is carried by one end of the plunger 335/25 346/141 opposite from the cover and in operation serves to make a se- [51 Int. Cl. ..G0ld 15/02 fies f indentations, usually in a binary code form, in a suitable Field of a h 8, 41, 1; /5 receptor sheet such as a pocket credit card. The plunger and 3/ 317/123 235/ 61-12; 335/255 cover are very light such that they can move rapidly under the influence of the magnetic field created when the solenoid is [56] Reierences Cited energized. The solenoid is initially energized and midway through the stroke of the plunger the driver current is cut off UNITED STATES PATENTS and the solenoid circuit remains closed through a diode such 1,155,501 10/1915 Moore ...346/ 141 X that the plunger continues accelerating towards the stop posi- 1,236,321 8/ 1917 Landon ...;346/l41 X tion under the influence of the decaying field of the magnetic ,107 6/1959 Wcingart et aL. --..346/ 140 X circuit. The efficiency of the device is high and the excess heat 3,243,665 3/ 1966 Fayel' et a]. 101/93 X generated is at a minimum. 3,325,632 6/1967 Lilly et a1 ..235/61.l2 3,504,623 4/1970 Staller 101/93 I 8 Claims, 6 Drawing Flgures Primary Examiner-Joseph W. l-lartary Attorney-Lee A. Strimbeck Patented Feb. 22, 1972 2 Sheets-Sheet 1 Tuhllll lH- INVENTORS JOHN G. WALLACE BY EDMUND SCHREINER ATTORNEYS.

Patented Feb. 22, 1972 2 Sheets-Sheet 2 TIMED PULSE GENERATOR FIG. 6.

INVENTORS JOHN G. WALLACE EDMUND SCHREINER Z I ATTzgR HIGH-SPEED lNDENTING RECORDER PRIOR ART US. Pat. No. 3,325,632 (Lilly) sets forth a method of encoding information by indenting a suitably supported magnetic film or strip with a series of fine indentations, usually in a binary code form. The fringe flux created by the indentations can be read in a conventional manner with a suitable reading head. This patent shows schematically the type of indenting recording head of interest here. 1

Patent application, Magnetically-Sensible Recording and Process of Producing the Same (Wallace), Ser. No. 855,501, filed Sept. 5, 1969, and now abandoned in favor of its continuation-in-part, Ser. No. 883,537, filed Dec. 9, l969, discloses an improvement on the Lilly method wherein a series of indentations are made in the surface that is not necessarily magnetic, which indentations are filled with a magnetically sensible material.

THIS INVENTION This invention is concerned with an electromechanical indenting recording device adapted to create a record in the manner of the Lilly patent or Wallace application. The present recorder is characterized by its quite small size and by its high efficiency and speed.

The prior art indenting recorders such as in Lilly were generally of low efficiency. Their efficiencies were less than 1 percent and therefore considerable excess heat was generated, which heat limited the speed of operation. The designs were bulky. The moving components of the recording heads, i.e., the indenting stylus and solenoid hammer, weighted as much as 0.02 pounds or more which limited the velocities that could be obtained with a given energy input and travel distance. The moving components of the present recording head preferably weigh less than 0.001 lbs.

Since the moving components of the recorder are quite light in weight, they can be accelerated to a much higher velocity than is usual which in turn decreases the; time required to make each indentation and the time required for current to be applied to the solenoid. The energy cycle of the present recorder is uniquely designed to maximize its efficiency and speed, and to keep heat losses to a minimum.

DRAWING The drawing is a greatly enlarged view of the recording head of this invention and shows in:

FIG. 1, a vertical cross section taken along the midplane;

F lg. 2, and end view of the device taken along the arm sectIon;

F lg. 3 is a bottom view. The small size of the component is indicated by the scale given on the drawing;

Fig. 4 is a circuit diagram; and

FIGS. 5 and 6 illustrate an alternative embodiment of the invention. like parts having the same number as in the other figures, and FIG. 5 being an elevation view and FIG. 6 is a sectional view taken along the line AA in FIG. 5.

DESCRIPTION Referring to the drawings, the recorder comprises a solenoid coil and a ferromagnetic coil housing 2 about the coil. The housing consists essentially of two parts, an outer shell or tube 2a and an inner tube or shell 2b, which tubes are of substantially equal cross-sectional areas and are joined at one end and open to the cover 5 at the other. A movable plunger 3 has attached thereto a cover 5 which extends over the housing 2 to form an airgap therewith and in a manner such that the housing serves as a stop for the plunger and cover when the plunger is at the point of maximum travel where indenting occurs. The plunger can be constructed of a material such as stainless steel or brass. The core is biased in a normally open position by spring 4. The face of plunger 3 carries an indenting knife 7 which extends beyond the housing when the plunger is in the maximum (stop) position so as to make the desired indentation in a suitable receptor sheet, a portion of which is shown at 9. This assembly is carried by a suitable arm 8 which has a relatively large surface area and is formed from a metal having a relatively good heat conductivity such as aluminum, such that the arm 8 serves as a heat sink and radiator.

A pin 10 keeps the knife 7 in proper angular orientation by registration at the cover 5. The cover 5, and housing 2 are preferably of a ferromagnetic material such as iron and form with air gap 6 a magnetic circuit. The air gap is an annular space about the axis of the device between the cover and coil housing and contains two magnetic flux paths through the air 11 & 12 each being an annulus of equal cross-sectional area. The complete magnetic flux path 13 is shown in FIG. 1.

The basic operation of the recorder is as follows: an external current is applied to the solenoid in a conventional manner (not shown) and creates a magnetic force in the airgap. This force accelerates the core 5 and plunger with the indenting knife into the receptor sheet 9 against the action of the spring. The spring returns the plunger to the rest or normally open position after cessation of the magnetic field.

It usually requires inthe order of 0.01 in-pounds in energy to make an indentation in a suitable cardboard or plastic receptor sheet. This energy can be obtained, for example, by a saturated magnetic field force of two pounds in a gap of 0.005 inches, assuming a negligible spring force. If all of this energy is converted into kinetic energy of the moving cover and plunger, then the impact energy E is k mv where m is the mass of the plunger cover and indenting knife and v is the terminal velocity. As m is made smaller for the same magnetic field force, v increases and the resulting greater velocity decreases the gap transit time. It is a feature of this invention that m be quite small, less than 0.001 pounds, so that this gap transit time is quite short. The recorder of this invention is capable of making in excess of 500 indentations per second. This speed is achieved without overheating.

The shorter gap transit time increases the efficiency of the device, of course, by diminishing the electrical loss per printing event because of the shorter time needed for. current flow in the solenoid.

The amount of current required is also optimally minimized according to this invention in the following manner. To achieve a minimum gap transit time it is desirable to keep the airgap magnetically saturated and thus obtain the highest acceleration of the plunger. It is not, however, required to keep the external current applied to the solenoid on during the entire stroke of the plunger in order to maintain a saturated field. When the gap is open, it takes a relatively large amount of energy to build up the magnetic field to its saturation level. The larger the inrush current, the shorter the time it takes to reach to the saturation level. Once saturation is reached, it takes less current to maintain the field. Also, as the airgap becomes small with the stroke of the plunger, less magnetic energy is required in the total circuit to maintain the saturated field.

FIG. 4 illustrates one suitable type of circuit. In FIG. 4, the solenoid coil is indicated at 1. It is connected to a driver 15, e.g., a square wave-timed pulse generator, in parallel with a resistor l6 and a diode 14.

If the external current source is disconnected, the magnetic field will decay rapidly and give rise to an induced current which will continue to flow in the same direction as the original current until the magnetic field is reduced to the residual field. This induced current will persist for the longest time at the highest level if during the period of field collapse the ends of the solenoid are shorted to each other as is approximated by a diode 14 in FIG. 4. This persisting induced current thus extends the duration of the magnetic field beyond the moment of shutoff of the externally applied power.

A point is reached, therefore, when the plunger is moving sufficiently fast that after switching off the external current supply from the driver 15, and allowing the current flow to continue through the diode 14, the resulting decay of the magnetic field parallels the decay of the field theoretically required to maintain saturation in the gap as the gap distance decreases to zero. According the this invention, this measured optimum point is the point at which the external current is shut off and the pulse width time of the driving circuit is set accordingly. The plunger is allowed to coast in an accelerating fashion to the stop position on the current flow produced by the decaying magnetic field. This considerably reduces the energy requirement of the device. A resistor 16 controls the decay time of the current.

The energy cycle of the device of this invention starts with a fast rise time high inrush current to the solenoid which builds up the magnetic saturation field. This field does work in accelerating the plunger 3 and in compressing spring 4. When saturation is reached, the current is allowed to decay exponentially to a point, and then is switched off. At this point the magnetic field becomes a source of EMF, the polarity across the diode reverses, the coil circuit is closed through the now conducting diode to allow the flow of the induced current to persist, and the decaying magnetic field continues to convert it energy into kinetic energy by accelerating the plunger and into potential energy of the compressed spring. Any magnetic energy not so converted degenerates into heat by different loss modes.

Thus, near. the moment of gap closure, the magnetic field energy in accordance to this invention is designed to be nearly exhausted and the kinetic energy of the plunger is at its maximum. The plunger at this moment of gap closure moves with a speed in the order of 100 inches per second. This'kinetic energy is largely dissipated when knife 7 makes the indentation, and any remaining kinetic energy is dissipated and converted to heat when the stop position is reached. After the stop position is reached, the potential energy of the compressed spring 4 which has reached its peak value, returns the plunger to its normally open position.

The above-described cycle is the most efficient cycle possible. The required energy to perform the function of making an imprint is at a minimum and almost no energy is wasted. All losses are limited to coil resistance loss, eddy current loss and hysteresis loss in the iron, friction losses and windage loss-of the moving plunger and damping loss in the spring. By avoidance of wasting energy, that will turn into heat, all heat generated in the recorder is now primarily a result of above losses. These losses are kept small in the manner of this invention. Overheating, as a result of the high printing rate is prevented by providing sufficient heat sinking capability for the recorder assembly. This is accomplished primarily by making the support arm for the coil housing 2 of a material with a high thermal conductivity such as aluminum. The arm 8 has a high surface area and allows a sufficientheat flow to the ambient air which can be aided as by forced convection from an air blower. Heat sinking can be improved by using a foil wound coil 1 instead ofa wire wound coil.

Optimum heat sinking is obtained by making the coil a single turn and dividing the arm to provide current paths to and from the coil, thus rendering the coil 1 and arm 8 a single component 17 as shown in FIGS. 5 and 6. Arm 8 is divided into two sections 8a and 8b to give the necessary current paths.

We claim:

1. An electromechanical indenting recorder comprising:

a. a solenoid coil;

b. a ferromagnetic housing about said coil;

c. a nonferromagnetic plunger within said coil movable along the axis of said coil from a normally open position to a stop position;

f. spring means operatively associated with said plunger to bias said plunger in said normally open position;

g. energizing means for energizing said magnetic circuit and magnetically saturate said airgap sufficient to cause said plunger and cover to accelerate towards said stop position against the resistance of said spring means, said energizing means including means to cease the flow of current and short circuit said coil when said plunger is moving from said normally open position towards said stop position in a position intermediate therebetween so that said plunger continues to said stop position under the influence of the decaying magnetic field in said magnetic circuit.

2; The recorder of claim 1 wherein said decaying magnetic field substantially parallels the field required to maintain satu- 4. The recorder of claim 1 wherein said housing is in thermally conductive contact with and is carried by a substantially larger mass of metal having a relatively large surface area that serves as a heat sink. 7 Y

5. The recorder of claim 4 wherein said coil and arm are combined into a single component with a single coil turn, the arm being divided to serve as two current paths to and from the coil.

6. In an electromechanical indenting recorder having a solenoid, a movable nonferromagnetic plunger therein, one end thereof carrying an indenting knife, a ferromagnetic housing about said solenoid, a ferromagnetic core cover attached to said plunger and forming with said housing an annular air gap about the axis of said plunger when said plunger is in a rest position, and a spring means biasing said plunger and cover in said rest position, said core, cover and housing forming with said air gap a magnetic circuit, said plunger and cover being adapted to being accelerated to an indenting position by the field created by said magnetic circuit when a current is applied to said solenoid, said cover coming to a stop position against said housing when said plunger reaches the maximum indenting position; the improved method of operation thereof comprising: initially applying current to said coil tocause said magnetic circuit rapidly to become saturated and to accelerate said plunger towards said indenting position against the resistance of said spring means, ceasing the flow of said current and short circuiting said solenoid when said plunger is moving at a position intermediate of said rest and stop positions and allowing said plunger to continue to said stop position under the influence of the resulting decaying magnetic field in said magnetic circuit.

7. The improvement of claim 6 wherein said decaying magnetic field maintains a saturated condition in said airgap such that said plunger continues to accelerate towards said stop position.

8. The improvement of claim 6 wherein said plunger is 

1. An electromechanical indenting recorder comprising: a. a solenoid coil; b. a ferromagnetic housing about said coil; c. a nonferromagnetic plunger within said coil movable along the axis of said coil from a normally open position to a stop position; d. a ferromagnetic cover attached to said plunger and extending at least in part over said housing forming an airgap therebetween, said cover serving to stop the movement of said plunger by contacting said housing and said coil, cover and housing forming a magnetic circuit with said airgap; e. an indenting knife carried by one end of said plunger opposite said cover and extending beyond said housing when said plunger is in said stop position; f. spring means operatively associated with said plunger to bias said plunger in said normally open position; g. energizing means for energizing said magnetic circuit and magnetically saturate said airgap sufficient to cause said plunger and cover to accelerate towards said stop position against the resistance of said spring means, said energizing means including means to cease the flow of current and short circuit said coil when said plunger is moving from said normally open position towards said stop position in a position intermediate therebetween so that said plunger continues to said stop position under the influence of the decaying magnetic field in said magnetic circuit.
 2. The recorder of claim 1 wherein said decaying magnetic field substantially parallels the field required to maintain saturation in said airgap.
 3. The recorder of claim 1 wherein said plunger, cover and indenting knife together weigh less than 0.001 pound.
 4. The recorder of claim 1 wherein said housing is in thermally conductive contact with and is carried by a substantially larger mass of metal having a relatively large surface area that serves as a heat sink.
 5. The recorder of claim 4 wherein said coil and arm are combined into a single component with a single coil turn, the arm being divided to serve as two current paths to and from the coil.
 6. In an electromechanical indenting recorder having a solenoid, a movable nonferromagnetic plunger therein, one end thereof carrying an indenting knife, a ferromagnetic housing about said solenoid, a ferromagnetic core cover attached to said plunger and forming with said housing an annular air gap about the axis of said plunger when said plunger iS in a rest position, and a spring means biasing said plunger and cover in said rest position, said core, cover and housing forming with said air gap a magnetic circuit, said plunger and cover being adapted to being accelerated to an indenting position by the field created by said magnetic circuit when a current is applied to said solenoid, said cover coming to a stop position against said housing when said plunger reaches the maximum indenting position; the improved method of operation thereof comprising: initially applying current to said coil to cause said magnetic circuit rapidly to become saturated and to accelerate said plunger towards said indenting position against the resistance of said spring means, ceasing the flow of said current and short circuiting said solenoid when said plunger is moving at a position intermediate of said rest and stop positions and allowing said plunger to continue to said stop position under the influence of the resulting decaying magnetic field in said magnetic circuit.
 7. The improvement of claim 6 wherein said decaying magnetic field maintains a saturated condition in said airgap such that said plunger continues to accelerate towards said stop position.
 8. The improvement of claim 6 wherein said plunger is returned to said rest position by said spring means, and the cycle is then repeated at a rate exceeding 500 times a second. 